Senior officials in Britain, France and Germany, the three European Union countries negotiating with Iran over its nuclear program, are warning the Islamic Republic that it faces international sanctions if it does not stop plans to resume nuclear activity.

European officials monitoring the negotiations with Iran are urging the Islamic Republic not to start nuclear activities that it froze under an agreement last November with the EU trio.

One senior British diplomat who has taken part in the talks says a statement Monday by the deputy head of Iran's Atomic Energy Organization that his country will resume activities related to uranium enrichment in the next few days would breach the agreement. The British diplomat warns that such a step would mean a collapse of ongoing negotiations and a referral of Iran's nuclear program to the U.N. Security Council.

In Berlin, a German diplomat familiar with the Iranian nuclear file says any resumption of nuclear activity on Iran's part would lead to a possible referral to the Security Council. If that happens, says the German diplomat, there is a danger that international sanctions will be imposed on Iran.

In Paris, a French foreign ministry official says that, as far as he knows, Iran has not made a decision to resume nuclear activities, but that France hopes it does not and decides instead to continue its dialogue with the EU trio.

The EU officials are wary about commenting publicly on Iran's plans, saying statements like those on Monday are meant to curry favor with a domestic Iranian audience in the run-up to presidential elections in Iran next month. But the British diplomat says he thinks hard-liners in Iran who, in his words, are seeking to provoke an international crisis and strengthen their own hand, may be responsible for the defiant tone emanating from Tehran.

The United States has long argued that Iran's nuclear energy program is a cover for its efforts to build a nuclear weapon and wants Iran referred to the Security Council. Iran says its program is designed only to produce electricity. The E.U. trio is trying to get Iran to give up enriching uranium, which can be used in both civil nuclear reactors or to make a bomb. In exchange, the trio is offering technological, political and commercial inducements to Tehran.

Nuclear proliferation expert Gary Samore, at London's International Institute for Strategic Studies, says Washington is prepared to support any agreement reached between the E.U. and Iran as long as it holds.

"If, on the other hand, the talks collapse and Iran resumes its enrichment program as it has threatened to do, then there's no doubt that the Europeans will join Washington and refer the matter to the Security Council," he said.

But Mr. Samore also says there is no clear indication of what action the Security Council might take if the case against Iran lands in its lap.

"I think a variety of proposals would be put forward for political and economic sanctions, but whether the Security Council, and, in particular, the Russians and Chinese, have an appetite for taking strong measures against Iran is just unclear at this point," he added.

The Iranians so far have not indicated that they will resume uranium enrichment, only the conversion of raw uranium into uranium gas. But that step is enough to spook the EU trio because uranium gas can be fed into enrichment centrifuges for purification into a fuel that can be used in reactors, or into bomb-grade material.